ARM: ZERO_PAGE: Avoid flush_dcache_page() for zero page

The zero page is read-only, and has its cache state cleared during
boot.  No further maintanence for this page is required.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --cc arch/arm/mm/fault-armv.c
Simple merge

diff --cc arch/arm/mm/flush.c
Simple merge

diff --cc arch/arm/mm/mmu.c
Simple merge